Amplifying system



Dec. 19, 1922. 4

P. D. LOWELL.

AMPLIFYING SYSTEM.

2 SHEETSSHEET 2 FILED SEPT. 9,1921.

Dec. 19, 1922.

P. n. LOWELL.

AMPLIFYING SYSTEM.

HLED SEPT. 9, 1921.

2 SPEETS-SHEET I.

I flu-mu,

Patented Dec. 19, 192 2.

UNITED STATES A 1,439,562 PATENT OFFICE.

PERCIVAL D. LOWELL, OI WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOR TO RADIO INSTRUMENT" COMPANY, INC., BIA, A CORPORATION OF DELAWARE.

OF WASHINGTON, DISTRICT OF COLUM- AMPLIFYING SYSTEM.

Application filed September 9, 1921.

To all whom it may concern.

Be it known that I, PEROIVAL D. LOWELL,

plification of radio frequency currents by thermionic vacuum tubes employed in the reception of radio telegraph and telephone signals and more particularly to an arrangement of radio frequency transformers associated with the circuits of the thermionic vacuum tubes. 1

One of the objects of the invention is to provide a construction'of transformer permitting the operation of radio frequency amplifiers efficiently at short wave lengths and which may be. constructed for operation at any desired wave length over a wide band of wave lengths.'-

Another object of the invention is to provide a radio frequency transformer construction in which the capacity between the windlngs 1s a minimum.

A further object is to provide a construction for variably coupling the primary and secondary windingsof the radio frequency transformer, whereby the coupling may be set so as to produce amplification at a par-.

ticular wave length only or within a limited band of wave lengths, for selective reception.

A still further object is to provide a construction wherein aminimum capacity between the windings and the core is present.

Another object is to provide'a transformer which is removable from thestages of the radio frequency amplifier to permit the ready substitution of a transformer having its windingsdesigned and its coupling set for the particular wave length or band of wave lengths which it is desired to receive;

Radio frequency amplification of received signals throu h several stages is more desir-v able at the radio receiver than initially rectifying the signal energy and then amplifying the audio-frequency component alone. In radio frequencyamplification the amplifier is quieter, that is, superfluous noises and induction from dynamos are not amplified to as great a degree and a clearer signal is obtained than in the case. of audio frequency amplification.

Serial 499,388.

In general there are'two methods of cou-' pling between the stages of a multi-stage radio frequency amplifier, namely, transformer coupling and resistance coupling.

Generally speaking transformer coupling is more desirable than resistance coupling because greater voltage amplification is produced per stage. It is true, however, that the transformer circuits must be approximately tuned to the particular wave length, or in proximity thereto, at which the radio frequency amplifier is to be operated, while the resistance coupled radio frequency amplifier although not producing as much radio frequency amplification. per stage is advantageous because of its broader range of useful wave lengths.

Heretofore in the art it has been customary to construct radio frequency transformers for couplin the several stages of vacuum tube amplifiers, in two principal types; one of the shell type in which the primary and secondary windings are wound one beneath the other on the central core of the shell frame; and-the other in which thin flat coils are. employed and the primary and secondary arranged adjacent with their fiat sides mutually parallel,

In the first construction there is inherently a high capacity between the two windings and a considerable capacity between turns as well as capacity to the core, all capacity effects restricting the wave length range of the transformer, and also the amplifyingefiect,

particularly at short wave lengths. In the second type there is also a considerable capacity between the primary and secondary and the transformer is inherently ineflicient at short wave lengths by reason of the 'restricted coupling between the primary and secondary windings due to itsv air core'and the small numberof turns which may be employed on the windings at short Wave lengths.

My invention will be more clearly understood by reference to thefollowing specification and accompanying drawings in which Figure 1 shows the connections of a multi-stage radio frequency amplifier together with a rectification stage and stages of audio frequencyamplification with the present construction of radio frequency transformer interposed between the radio frequency stages of the thermionic vacuum tubes; Figure 2 is a perspective view of the radio frequency transformer; Figure 3 is a side view of the transformer showing the windings closely coupled; Figure 4 is a side view of the transformer with the primary and secondary windings more loosely coupled; Figure 5 is a schematic diagram showing the electricalconnections of the primary and secondary windings of the transformer; Figure 6 is a perspective view showing the completed transformer removably mounted on the rear of the vacuum tube panel; and Figure 7 is a modified form of transformer construction.

Referring particularly to Fig. 1 of the drawings, a multi-stage thermionic vacuum tube amplifier is shown comprising two stages of radio frequency amplification, a rectification stage and two stages of audio frequency amplification. When used as a receiver of radio telegraph or telephone signals the inductance 1 is coupled to the radio frequency receiving circuit such as an antenna ground circuit, or a loop system may be employed as a collector of energy. The inductance is shunted by variable condenser 2 and connected in the input circuit of vacuum tube 3 forming the first stage of radio frequency amplification. The output circuit of vacuum tube 3 is connected to the primary winding 7 of the radio frequency transformer 6. The radio frequency transformer has its primary winding 7 adjacent secondary winding 8 and disposed on iron core 9. The secondary winding 8 connects to the input circuit of vacuum tube 4 forming the second stage of radio frequency amplification. The output circuit of vacuum tube 4 is connected to the primary winding 11, of radio frequency transformer 10, having secondary winding 12 and the iron core 14. The secondary winding 12 of the second radio frequency transformer through grid leak 17 and grid condenser 16 with the input circuit of vacuum tube 15 forming the rectification stage of the amplifier. The output circuit of the vacuum tube 15. contains the audio frequency transformer 18, which connects with the input circuit of vacuum tube 20 which is in turn connected through audio frequency transformer 21 with the input circuit of vacuum tube 22, these last tubes 20 and 22 forming stages of audio frequency amplification. The-plate potential for all of the tubes is supplied from battery 13 and the filament lighting current for the several tubes from battery A. However. different potentials may be supplied to'the plate circuits of the rectification stage -and the-amplifier stages if desired. A variable resistance 5 is connected in circuit to vary the potential of the grids of vacuum tubes 3 and 4 of the radio frequency amplifier.

The construction of the radio frequency connects V transformers which are connected in the radio frequency stages of the amplifier circuit shown in Fig. 1 is represented in perspective view in Fig. 2. The transformer comprises insulated rectangular coil supports 25 and 28 which are relatively movable on the iron core 9 consisting of extremely thin laminations of enameled sheet silicon steel 24. The coil supports 25 and 28 contain slots 26 and 29 respectively, separated from adjacent slots by spaces 27 and 30 respectively. The primary and secondary windings are disposed upon the supports 25 and 28 respectively, the primary winding 7 being wound in slots 26 from one end of'the coil support to the other, the winding in one slotbeing completed before the beginning of the winding in the next adjacent slot 26. The secondary coil 8 is formed on support 28 by a winding in slots 29, the winding being completed in one slot and then progressing to the next adjacent slot.

The coil supports 25 and 28 maybe vari-. ablycoupled relative to each other. In Fig. 3 the windings are shown relatively tightly coupled while in Fig. 4 the primary and secondary windings are shown more loosely coupled to meet conditions in the reception of a particular frequency only, or over a limited range of frequencies.

Fig. 5 is schematic diagram of the primary and secondary windings of the transformer. The primary winding 7 which is connected to the radio frequency output circuit of one vacuum tube comprises anumber of spaced coil sections, all'of which may be relatively positioned with reference to the secondary winding 8 which connects to the input circuit of the succeeding vacuum tube. The secondary consists of a number ofparallel spaced coil sections which by reason of their winding in the slotted coil support may be adjustably coupled relative to the primary winding.

The radio frequency transformer is wound and its coupling fixed for a particular wave length or limited band of wave lengths which it is-desired to receive. For different wave lengths over a broad band, the number of turns in the windings of the radio frequency transformer must be selectively chosen. In adapting the amplifier circuit of Fig. 1 for operation upon all wave lengths means are provided by which the radio frequency transformers for operation on the particular wave length band to be received may be readily inserted or removed. Fig. 6 shows one form of mounting for the completed radio frequency transformer with relation to the vacuum tube of the amplifier stage. The completed transformer is shown at 31 enclosed in a rectangular insulated casing with insulated end closures 32. The terminals of the primary winding 7 are brought out at contacts 33 and 34, while the terminals of the secondary winding 8 are brought out to'contacts 35 and 36, whereby the entire rectangular case including the transformer and the contact terminals may be sprung into connecting clips 45, 46, 47 and 48. These connecting. clips are secured to the rear of vacuum .tube panel 41, which is vertically arranged and slotted at its top and bottom ends at 42 and 49 on the opposite sides of which spring clips 43 and 44 are arranged to form both supports for the vacuum tube 40 and also a means for securing electrical connections for the filament terminals and the grid and plate electrodes of the vacuum tube 40. Transformers for any wave lengths, constructed in accordance with this invention may be quickly inserted on the back of the panel and contacts made through clips 33-45, 3446, 35-47 and 35-48.

Other forms of plug-in mountings may be provided wherein fixed contacts connected with the electron tube circuits cooperate with a similar number of contacts carried by a transformer casing and connected to the winding therein, and I intend no limitations by the accompanying illustrative showing of one form of the invention.

Fig. 7 is a modification of the radio frequency transformer in which the primary and secondary windings are disposed on coil support 50 which encloses iron core 9. The primary winding comprises coils wound in slots onthe coil support and alternately connected as represented'at 51. The secondary winding comprises coils 52 Wound in slots alternately positioned between the coils 51. The entire transformer may be readily mounted and enclosed in the casing represented in Fig. 6 by reference character 31.

By the particular construction of this transformer the total inherent capacity of the winding is small, for the reason that.

the several capacities are series connected. The capacity of the windings with respect to the core is much smaller than in other types of transformers in thatthere is a minimum area of the winding immediately adjacent the core.

While I have described my invention in certain preferred forms and specific embodiments I do not wish to be restricted to these I forms, but merely intend to be limited withductive coupling means may be quickly removed or inserted in said supporting means, said fixed terminals and cooperating terminals being thereby mechanically contacted for comp eting the input and output circuits of the electron tubes through the several stages.

2. In a radio frequency thermionic electron tube amplifier, the combination of a plurality of amplifying stages, transformer supports, transformers selectively respon sive to particular wave lengths, fixed terminals on said supports, cooperating terminals on said transformers, contact faces on said terminals whereby said transformers may be quickly inserted or removed from said supports, the faces of said last mentioned terminals contacting with the faces of said first mentioned terminals for coupling the several stages.

3. In a radio frequency thermionic vacuum tube amplifier, the combination of a plurality of amplifying stages, transformer supports, radio frequency transformers having means for setting their coupling for selective operation of said amplifier at a particular frequency, terminals on said support, terminals on said transformers, contact faces on said terminals whereby said transformers may be quickly detached or plugged into said supports, the faces of said last mentioned terminals contacting with the faces of said first mentioned terminals for coupling the several stages.

4. In an amplifying system the combination of a plurality of electron tube stages a plurality of radio frequency transformers each responsive to particular bands of frequencies, a single resilient means for both mechanically-holding and electrically con necting said radio frequency transformers with said electron tube stages whereby said transformers may be quickly removed or inserted in said means, breaking or completing the electrical connections between said stages.

5. In a radio frequency electron tube amplifier, the combination of a plurality of electron tubes having grid filament and plate electrodes, an input circuit and an out put circuit including the electrodes of each of said tubes and means detachably plugged in between the output circuit of one tube and the input circuit of the succeeding tube for-transferring a particular band of frequencies from said output circuit to said input circuit, a plurality of separate means responsive to different bands of frequencies and means whereby said separate means can be quickly substituted for said first mentioned means upon detachment of said first mentioned means.

6. In a radio frequency electron tube amplifier, the combination of a plurality of electron tubes having grid filament and plate electrodes, an input circuit and an outfirst mentioned terminals whereby said electron tubes amplify dilii-u'cnt bands of radio 10 frequenc energy.

7. In an amplifying system the combination of a plurality oi' vacuum tube stages,

transformer supports, resilient means carried by said supports, a plurality of transformers, contacts 'on whereby said transformers may be quickly plugged in or removed from said supports causing the contacts on said transformers to cooperate with said resilient means on said said transformers] supports for completing the electrical con- 20 nections between said stages.

PERCIVAL D. LOWELL. 

